Dielectric element and manufacturing method therefor

ABSTRACT

A ferroelectric element having a high Pr and a low Ec and having a good withstand voltage, which is in the form of a thin film using a ferroelectric layer containing insulating particles, is provided. The ferroelectric layer containing the insulating particles is effective to suppress leakage current caused through grain boundaries of crystals, and hence to exhibit a high Pr and a low Ec and a good withstand voltage. The ferroelectric element has a structure in which such a ferroelectric layer in the form of a thin film is sandwiched between electrodes. By incorporating the ferroelectric element in a field effect transistor structure, it is possible to realize a highly integrated semiconductor device for detecting reading or writing.

TECHNICAL FIELD

The present invention relates to a ferroelectric element such as anFeRAM utilizing a non-volatile property of a ferroelectric material, asemiconductor device using the ferroelectric element, and a method ofmanufacturing the ferroelectric element. The present invention alsorelates to a high dielectric element such as a DRAM utilizing a highdielectric constant and a low leakage current density, a semiconductordevice using the high dielectric element, and a method of manufacturingthe high dielectric element.

BACKGROUND OF THE INVENTION

As a semiconductor memory, there is a DRAM (Dynamic Random AccessMemory) having the ability of rewriting data at a high speed. DRAMs havebeen produced which have a large capacity of 16 M bits to 64 M bits inresponse to the progress of these technologies for realizing a higherdensity and a higher integration. Such large capacity also requires atechnology for achieving finer geometries for circuit components,particularly, finer geometries for capacitors for storing information.For achieving finer geometries for capacitors, it is required to providea thin dielectric film, to select a material having a high dielectricconstant, and to change the structure of the capacitor composed of upperand lower electrodes and a dielectric material from two-dimensional tothree-dimensional. With respect to a high dielectric material, it isknown that BST (Ba/Sr)TiO₃ having a simple lattice perovskite crystalstructure exhibits a dielectric constant (ε) larger than that ofSiO₂/Si₃N₄. An example of the use of such a high dielectric material hasbeen reported in International Electron Device Meeting Technical Digest(IEDM Tech. Dig.), p. 823, 1991.

A non-volatile memory FeRAM (Ferroelectric Random Access Memory) using aferroelectric material as a capacitor material has a characteristiccapable of storing data in the OFF state of a power supply because itutilizes two residual polarization states which are different inpolarity. The FeRAM has a feature in terms of rewriting data at a speedwhich is very high, such as the order of μs or less, and therefore, itis expected to provide an ideal memory in the next generation. In thecase of such a FeRAM, it is also required to provide a thinferroelectric film for achieving a large capacity. Incidentally, asemiconductor memory intended to suppress reactivity between aferroelectric material and a metal electrode has been disclosed inJapanese Patent Application Laid-open No. 5-190797, in which PZT (leadzirconate titanate) is used as a ferroelectric material and a siliconnitride (SiNx) film operating as a diffusion preventive layer is formedaround the ferroelectric material.

SUMMARY OF THE INVENTION

The above-described technologies, however, have failed to examine thesuppression of the leakage current density accompanied by thinning of adielectric material essentially to be performed for increasing thedegree of integration. A memory using the above-described BST has theobject of lowering an operational voltage along with higher integration.For lowering the operational voltage of a memory, it is required toensure a sufficient capacitance at a small voltage. To increase such acapacitance, it has been proposed to select a material having a highdielectric constant, to increase the electrode area, and to make thehigh dielectric material thin. A thin film made of BST having apolycrystalline structure, however, has a problem in terms of withstandvoltage characteristic because such a polycrystalline film allowsleakage current to easily flow through grain boundaries of the crystals.For this reason, in the case of using the BST thin film as a capacitor,it is difficult to apply a sufficient operational voltage thereto.

In the above described ferroelectric capacitor, in which a siliconnitride film is formed around the PZT film, the silicon nitride filmacts as a diffusion preventive layer capable of preventing thermaldiffusion from elements of PZT, thereby maintaining a desirablestoichiometric composition of the ferroelectric material necessary forferroelectric characteristics. The silicon nitride layer in theabove-described ferroelectric capacitor, however, has a problem. Sincethe silicon nitride film has a dielectric constant as small as 7, itmust be formed to an ultra-thin thickness of 30 Å or less forsuppressing a lowering of the total capacitance of the ferroelectriccapacitor having a size of 4 μm². Further, in the case of a higherintegration in the order of 1 G bits, the area of the capacitor becomesas small as 0.1 μm². In this case, it becomes apparent on the basis ofsimple calculation that the silicon nitride layer must be formed to afurther ultra-thin thickness of 1 Å or less.

Additionally, in the thinning process used in the prior technologies, ifa metal is as an electrode, there occurs a problem that a transitionlayer is formed by diffusion of an element at an interface between adielectric thin film and the metal electrode, to thereby reducespontaneous polarization (Pr), to increase field reversing (Ec), and togive rise to film fatigue.

To solve the above-described problems, the present invention has beenmade, and an object of the present invention is to provide a highdielectric layer containing insulating particles, which is capable ofsuppressing leakage current flow through grain boundaries of crystalsand which can be thinned to such an extent as to meet a requirement ofhigh integration; a high dielectric element in which the high dielectricthin film is sandwiched between upper and lower electrodes; asemiconductor device using the high dielectric element; and a method ofmanufacturing the high dielectric element.

Another object of the present invention is to solve the above-describedproblems and to provide a ferroelectric layer containing insulatingparticles, which is capable of suppressing leakage current flow throughgrain boundaries of crystals and which can be thinned to such an extentas to meet a requirement of high integration; a ferroelectric element inwhich the ferroelectric thin film is sandwiched between upper and lowerelectrodes; a semiconductor device using the ferroelectric element; anda method of manufacturing the ferroelectric element.

A further object of the present invention is to provide a highdielectric element or a ferroelectric element including the abovementioned high dielectric thin film or the above mentioned ferroelectricthin film having a thickness of 200 Å or more, wherein the element canbe supplied with an operation voltage of 2 V for operating asemiconductor memory.

A further object of the present invention is to provide a highdielectric element in which a conductive oxide is used as an electrodewhich is in contact with the above mentioned high dielectric thin filmto suppress formation of a transition layer, and a method ofmanufacturing the high dielectric element.

A further object of the present invention is to provide a ferroelectricelement in which a conductive oxide is used as an electrode which is incontact with the above mentioned ferroelectric thin film to suppressformation of a transition layer, and a method of manufacturing theferroelectric element.

To achieve the above objects, according to the present invention, thereis provided a ferroelectric element including an upper electrode, aferroelectric thin film, and a lower electrode, wherein theferroelectric layer contains insulating particles having a resistance of10⁶ Ω or more.

According to the present invention, there is provided a high dielectricelement including an upper electrode, a high dielectric thin film, and alower electrode, wherein the high dielectric layer contains insulatingparticles having a resistance of 10⁶ Ω or more.

The insulating particles have particle sizes each being in a range of 50Å or less.

The ferroelectric thin film may be made of a material selected from thegroup consisting of a material expressed by(Pb_(1−x)A_(x))(Zr_(1−y)Ti_(y))O₃ (where A is one element selected fromthe group consisting of La, Ba, and Nb), and a material expressed by(AO)²⁺(B_(y−1)C_(y)O_(3y+1))²⁻ (where A is at least one element selectedfrom the group consisting of Tl, Hg, Pb, Bi, and a rare earth element; Bis at least one element selected from the group consisting of Bi, Pb,Ca, Sr, and Ba; and C is at least one element selected from the groupconsisting of Ti, Nb, Ta, W, Mo, Fe, Co, Cr and Zr; and y=2, 3, 4, and5).

The high dielectric thin film may be made of one material selected fromthe group consisting of a material expressed by (Ba_(1−x)Sr_(x))TiO₃ anda material expressed by (Pb_(1−x)A_(x))(Zr_(1−y)Ti_(y))O₃ (where A isone element selected from the group consisting of La, Ba and Nb).

The insulating particles may be those of a compound containing Si.

The lower electrode may be composed of a metal, a conductive oxide of asingle element, and a conductive oxide having a perovskite structure,which are formed on a base substrate in this order, and each of theconductive oxides may be oriented along a specific plane.

The upper electrode may be composed of a conductive oxide having aperovskite structure and a metal or it may comprise a conductive oxidehaving a perovskite structure, a conductive oxide of a single element,and a metal, which are formed in this order from the side in contactwith the ferroelectric thin film or the high dielectric thin film.

In the case where the ferroelectric thin film has a thickness of 200 Åor more, the ferroelectric element may exhibit a withstand voltage of 2V or more at a leakage current density of 10⁻⁵ A/cm² or less.

In the case where the high dielectric thin film has a thickness of 200 Åor more, the high dielectric element may exhibit a withstand voltage of2 V or more at a leakage current density of 10⁻⁵ A/cm² or less.

The metal used for the electrode may be at least one metal selected fromthe group consisting of Pt, Au, Al, Ni, Cr, Ti, Mo, and W. Also, torealize the function of the electrode material, a conductive oxide of asingle element or a perovskite structure, which has a resistivity of 1mΩ·cm or less, may be used as the electrode. The conductive oxide of asingle element may be an oxide of at least one element selected from thegroup consisting of Ti, V, Eu, Cr, Mo, W, Rh, Os, Ir, Pt, Re, Ru and Sn.The conductive oxide having a perovskite structure may be at least onekind of perovskite oxide selected from the group consisting of ReO₃,SrReO₃, BaReO₃, LaTiO₃, SrVO₃, CaCrO₃, SrCrO₃, SrFeO₃,La_(1−x)Sr_(x)CoO₃ (0<x<0.5), LaNiO₃, CaRuO₃, SrRuO₃, SrTiO₃, andBaPbO₃, and has a resistivity of 1 mΩ·cm or less.

According to the present invention, there is provided a method offorming the ferroelectric thin film, including the step of forming theferroelectric thin film by sputtering in an atmosphere of a mixed gas ofoxygen and an inert gas at a temperature of 650° C. or less. Inaddition, the film formation temperature is selected to suppressreaction with an electrode. Instead of the sputtering method describedabove, the ferroelectric thin film may be formed by MOCVD in anatmosphere of oxygen or excited oxygen at a temperature of 650° C. orless.

According to the present invention, there is provided a method offorming a ferroelectric thin film, including the step of forming theferroelectric thin film by applying a starting material composed of ametal alkoxide or a metal salt of an organic acid on a substrate byspin-coating or dip-coating and baking the film at a normal pressure andat a temperature of 650° C. or less. In addition, the film formationtemperature is selected to suppress a reaction with the electrode.

According to the present invention, there is provided a method offorming a high dielectric thin film, including the step of forming thehigh dielectric thin film by sputtering in an atmosphere of a mixed gasof oxygen and an inert gas at a temperature of 650° C. or less. Inaddition, the film formation temperature is selected to suppressreaction with the electrode. Instead of the sputtering method describedabove, the high dielectric thin film may be formed by MOCVD in anatmosphere of oxygen or excited oxygen at a temperature of 650° C. orless.

According to the present invention, there is provided a method offorming a high dielectric thin film, including the step of forming thehigh dielectric thin film by applying a starting material composed of ametal alkoxide or a metal salt of an organic acid on a substrate byspin-coating or dip-coating and baking the film at a normal pressure andat a temperature of 650° C. or less. In addition, the film formationtemperature is selected to suppress a reaction with the electrode.According to the present invention, there is provided a method offorming the conductive oxide of a single element or a perovskitestructure, including the step of forming a conductive oxide of a singleelement or a perovskite structure by sputtering in an atmosphere of amixed gas of oxygen and an inert gas at a temperature of 650° C. orless. Instead of the sputtering method described above, the conductiveoxide of a single element or the perovskite structure may be formed byMOCVD in an atmosphere of oxygen or excited oxygen at a temperature of650° C. or less.

According to the present invention, there is provided a method offorming the conductive oxide of a single element or the provskitestructure, including the step of forming the conductive oxide of asingle element or the provskite structure by applying a startingmaterial composed of a metal alkoxide or a metal salt of an organic acidon a substrate by spin-coating or dip-coating and baking the film at anormal pressure and at a temperature of 650° C. or less. In addition,the film formation temperature is selected to suppress a reaction withan electrode.

Further, in the step of forming the ferroelectric thin film from astating material composed of a metal alkoxide or a metal salt of anorganic acid by spin-coating or dip-coating, the ferroelectric thin filmmay be formed while irradiating ultraviolet rays to the ferroelectricthin film. This is based on the knowledge that the decomposition of araw material caused by light irradiation is considered effective forlowering the film formation temperature. The high dielectric thin filmmay be also formed while irradiating ultraviolet rays to the highdielectric thin film in the same manner as described above, and further,the conductive oxide may be formed while irradiating ultraviolet rays tothe high dielectric thin film in the same manner as described above.

According to the present invention, there is provided a semiconductordevice, wherein the structure including the upper electrode, theferroelectric thin film, and the lower electrode is formed as acapacitor in a structure of a field effect transistor.

Further, according to the present invention, there is provided asemiconductor device, wherein the structure including the upperelectrode, the high dielectric thin film, and the lower electrode isformed as a capacitor in a structure of a field effect transistor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of a ferroelectric layer of the present invention;

FIG. 2 is a diagram of a prior art ferroelectric layer;

FIG. 3 is a sectional view showing a ferroelectric element of thepresent invention;

FIG. 4 is a sectional view showing a high dielectric element of thepresent invention;

FIG. 5 is a photograph by a TEM, showing the ferroelectric layer of thepresent invention;

FIG. 6 is a graph showing data on a leakage current density of theferroelectric element of the present invention;

FIG. 7 is a sectional view showing an internal configuration of a lowerelectrode of the present invention;

FIGS. 8(a) and 8(b) are sectional views showing an internalconfiguration of a lower electrode of the present invention;

FIG. 9 is a sectional view showing a semiconductor device using theferroelectric element of the present invention; and

FIG. 10 is a graph showing a relationship between film thickness and thewithstand voltage characteristic for the ferroelectric element of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The present invention, however, is notlimited thereto.

In addition, reference numerals in the drawings are as follows:

Each of reference numerals 31, 41, 81, 91 indicates an upper electrode;each of the reference numerals 32, 71, 81, and 92 denotes aferroelectric thin film; reference numeral 42 denotes a high dielectricthin film; each of the reference numerals 33, 43, 83, and 93 denotes alower electrode; each of the reference numerals 34, 44, and 75 denotes abase substrate; each of the reference numerals 72 and 82 denotes aconductive oxide having a perovskite structure; each of the referencenumerals 73 and 83 denotes a conductive oxide of a single element; eachof the reference numerals 74 and 84 denotes a metal; each of thereference numerals 94 and 96 denotes a SiO₂ film; reference numeral 95denotes Si; numeral 97 denotes a diffusion layer; numeral 98 denotes agate electrode; and numeral 99 denotes a SiO₂ gate film.

Embodiment 1

FIG. 1 is a view showing a structure including an upper electrode 11, aferroelectric layer 13, and a lower electrode 12 according to thepresent invention. In the ferroelectric layer 13, insulating particles16 containing Si are precipitated at crystal grain boundaries 15 betweencrystals 14 of a ferroelectric material. Such a structure makes itpossible to suppress reduction in withstand voltage characteristic whichis, as shown by a comparative example in FIG. 2, due to a leakagecurrent 21 flowing through grain boundaries of crystals of aferroelectric material, and, hence, it is possible to apply anoperational voltage essential for operation of a memory. Further, sinceparticle sizes of the insulating particles are each in a range of 50 Åor less, the insulating particles exert only a small effect on thecapacitance of a capacitor even if the insulating particles have adielectric constant smaller than that of the dielectric material. As aresult, a capacitor having such a structure can provide a capacitance ofmore than 30 fF necessary for a DRAM.

Next, there will be described a method of preparing a ferroelectric thinfilm made from a material expressed by a chemical structural formula of(AO)²⁺(B₁C₂O₇)²⁻ where A=Bi, B=Sr, and C=Ta. In a sectional view of aferroelectric element as shown in FIG. 3, reference numeral 34 indicatesa base substrate. First, as the base substrate 34, there was used a Siwafer on which a TiN layer as a barrier layer was formed to a thicknessof 200 Å at a temperature of 300° C. and a SiO₂ layer was formed thereonby thermal oxidation. Then, a base electrode 33 was formed on the basesubstrate 34. As the backing electrode, a Pt thin film was formed to athickness of 1,000 Å by sputtering at a temperature of 350° C. Aferroelectric thin film 32 was then formed on the lower electrode 33 asfollows. First, a solution of alkoxides of Bi, Sr, Ta, and Si wasapplied on the lower electrode 33 by spin-coating at 1,500 rpm for 30sec, the electrode was dried at 150° C. for 5 min, and then it wassubjected to pre-heat treatment in air or oxygen at a temperature of 200to 550° C. lower than a crystallization temperature of the ferroelectricthin film, that is, 580° C. for 10 to 30 min. Such a procedure was takenas one cycle, and the cycle was repeated 2-5 times, to form a precursorthin film having a thickness of 1,000 Å. The precursor thin film wasfinally heat-treated at a temperature of 580 to 650° C., to obtain aferroelectric layer of (Bi₂O₂)²⁺(SrTa₂O₇)²⁻ containing an amorphous Sicompound.

The ferroelectric layer thus obtained was observed by a TEM, which gavea result as shown in FIG. 5. As is apparent from FIG. 5, amorphousparticles having particle sizes each in a range of 20 to 50 Å wererecognized between crystals of the ferroelectric material havingparticle sizes each in a range of 100 to 1,000 Å. The amorphousparticles were those of a compound containing Si, Bi, Sr and Ta. Thecomposition of the compound was largely dependent on the state of theparticles.

A result of examining a relationship between a voltage and a leakagecurrent density for such a ferroelectric element is shown in FIG. 6. Fora ferroelectric element containing no particles, a leakage currentdensity was as large as 10⁻⁴ A/cm² at 1 V. As a result, a ferroelectricelement could not used as a capacitor. On the contrary, for theferroelectric element containing particles, the leakage current densitywas very small, such as 1×10⁻⁷ A/cm² or less at 5 V. This shows that theferroelectric element containing particles exhibits a very goodwithstand voltage characteristic. The ferroelectric element containingparticles also exhibited good ferroelectric characteristics. That is,2Pr was 16 μC/cm² at 3 V, Ec was 40 kV/cm, and degradation of thecharacteristics was about 3% after writing 10¹⁵ times bypositive/negative reversal of a voltage of 3 V. Consequently, in theferroelectric element containing particles, reduction in characteristicsdue to precipitation of particles was not recognized.

A relationship between a film thickness and a withstand voltagecharacteristic for the ferroelectric layer of (Bi₂O₂)²⁺(SrTa₂O₇)²⁻containing the above insulating particles is shown in FIG. 10. Sampleseach having a film thickness of 200 to 2,000 Å were prepared by changingthe above-described cycle of the procedure for forming a precursor thinfilm. As is apparent from FIG. 10, the withstand voltage was 2 V or moreat the leakage current density of 10⁻⁵ A/cm² for the samples each havinga film thickness of 200 Å or more.

Although in the above embodiment (Bi₂O₂)²⁺(SrTa₂O₇)²⁻ is used as theferroelectric material, a solution of an alkoxide of Si may be added toa ferroelectric material having a perovskite crystal structure expressedby a chemical structural formula of (AO)²⁺(B_(y−1)C_(y)O_(3y+1))²⁻ wherethe A site is at least one element selected from the group consisting ofTl, Hg, Y, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; the Bsite is at least one element or more selected from the group consistingof Bi, Pb, Ca, Sr, and Ba; the C site is at least one element or moreselected from the group consisting of Ti, Nbi Ta, W, Mo, Fe, Co, Cr, andZr; and y=2, 3, 4, and 5.

Further, another ferroelectric thin film 32 was formed on the lowerelectrode 33 obtained in the same manner as described above. First, asolution of alkoxides of Pb, Zr, Ti, and Si was applied on the lowerelectrode 33 by spin-coating at 1,500 rpm for 30 sec, the electrode wasdried at 150° C. for 5 min, and then it was subjected to pre-heattreatment in air or oxygen at a temperature of 200 to 400° C. lower thana crystallization temperature of the ferroelectric thin film, that is,450° C. for 10 to 30 min. Such a procedure was taken as one cycle, andthe cycle was repeated 2-5 times, to form a precursor thin film having athickness of 1,000 Å. The precursor thin film was finally heat-treatedat a temperature of 500 to 650° C., to obtain a ferroelectric layer ofPb(Zr_(0.5)Ti_(0.5))O₃ containing an amorphous Si compound. For, thisferroelectric element containing particles, the leakage current densitywas very small, such as 1×10⁻⁷ A/cm² or less at 5 V. This shows that theferroelectric element exhibits a very good withstand voltagecharacteristic. The ferroelectric element also exhibited goodferroelectric characteristics. For example, 2Pr was 40 μC/cm² at 3 V, Ecwas 60 kV/cm, and degradation of characteristics was about 3% afterwriting 1012 times by ± reversal of a voltage of 3 V. Consequently,reduction in characteristics due to precipitation of particles was notrecognized. Further, with respect to the dependency of the filmthickness on the withstand voltage, the withstands voltage was 2 V ormore at the leakage current density of 10⁻⁵ A/cm² for the samples eachhaving a thickness of 200 Å or more.

Although in the above embodiment Pb(Zr_(0.5)Ti_(0.5))O₃ is used as theferroelectric material, a solution of an alkoxide of Si may be added toa ferroelectric material having a perovskite crystal structure expressedby a chemical structural formula of (Pb_(1−x)A_(x))(Zr_(1−y))Ti_(y))O₃where the A site is substituted for at least one element or moreselected from a group consisting of La, Ba, and Nb; and each of x and yis in a range of 0 to 1.

Embodiment 2

Next, there will be described a method of preparing a high dielectriclayer having a crystal structure expressed by (Ba_(0.5)Sr_(0.5))TiO₃ inthis embodiment. In a sectional view of a high dielectric element asshown in FIG. 4, reference numeral 44 indicates a base substrate. As thebase substrate, there was used a Si wafer on which a TiN layer as abarrier layer was formed to a thickness of 200 Å at a temperature of300° C. and a SiO₂ layer was then formed by thermal oxidation. Then, alower electrode 43 was formed on the base substrate 44. As the lowerelectrode, a Pt thin film having a thickness of 1,000 Å was formed bysputtering at a temperature of 350° C. A high dielectric thin film 42was formed on the lower electrode 43 as follows. First, a solution ofalkoxides of Ba, Sr, Ti, and Si was applied on the lower electrode 43 byspin-coating at 1,500 rpm for 30 sec, the electrode was dried at 150° C.for 5 min, and then it was subjected to pre-heat treatment in air oroxygen at a temperature of 200 to 550° C. lower than a crystallizationtemperature of the ferroelectric thin film, that is, 580° C. for 10 to30 min. Such a procedure was taken as one cycle, and the cycle wasrepeated 2-5 times, to form a precursor thin film having a thickness of1,000 Å. The precursor thin film was finally heat-treated at atemperature of 580 to 650° C., to thus obtain a high dielectric layer of(Ba_(0.5)Sr_(0.5))TiO₃ containing an amorphous Si compound. The highdielectric layer thus obtained was observed by a TEM, which gave aresult in which amorphous particles having particle sizes each in arange of 20 to 50 Å were recognized between crystals of the highdielectric material having particle sizes each in a range of 100 to 500Å. The particles were those of a compound containing Si, Ba, Sr and Ti,and the composition of the compound was largely dependent on the stateof the particles. As a result of examining a relationship between thevoltage and leakage current density for the high dielectric element, itwas found that the leakage current density was very small, such as1×10⁻⁷ A/cm² or less at 3 V. This shows that the ferroelectric elementcontaining particles exhibits a very good withstand voltagecharacteristic. The ferroelectric element also exhibited a dielectricconstant (ε) of 250 at a frequency of 1 MHz which was larger than thatof SiN_(x), and consequently, it was found that degradation ofcharacteristics due to precipitation of particles was not recognized.With respect to the dependency of the film thickness on the withstandvoltage, the withstand voltage was 2 V or more at the leakage currentdensity of 10⁻⁵ A/cm2 for the high dielectric thin film having athickness of 200 Å or more.

Although in the above embodiment (Ba_(0.5)Sr_(0.5))TiO₃ is used as theferroelectric material, a solution of an alkoxide of Si may be added toa high dielectric material having a perovskite crystal structureexpressed by a chemical formula of (Ba_(1−x)Sr_(x))TiO₃ where x isadjusted in a range of 0 to 1.

Embodiment 3

FIG. 7 is a view showing an internal configuration of a lower electrodein this embodiment. The lower electrode includes a metal 74, aconductive oxide 73 of a single element, and a conductive oxide 72having a perovskite structure. Although in each of the embodiments 1 and2, a metal electrode was used as the lower electrode, a lower electrodein contact with a ferroelectric material is made from a conductive oxidehaving a perovskite structure in this embodiment. Such a lower electrodewas effective to suppress an oxygen loss layer having been generallyrecognized at an interface between a ferroelectric material and a metalelectrode, and hence to suppress lowering of Pr due to reversal ofvoltage. In formation of this lower electrode, the metal, conductiveoxide of a single element, and conductive oxide having a perovskitestructure were laminated in this order on a base substrate. This waseffective to improve the adhesiveness between adjacent ones of thelayers. This was also effective to control orientation of the conductiveoxide having a perovskite structure and hence to form a ferroelectricthin film or a high dielectric thin film on the conductive oxide whilecontrolling the orientation of the thin film. Hereinafter, there will bedescribed a method of preparing the lower electrode. First, the metal 74represented by Ru was formed on the above-described base substrate 34 toa thickness of 1,000 Å by sputtering at a temperature of 600° C.; theconductive oxide 73 of a single element represented by RuO was formedthereon to a thickness of 1,000 Å by sputtering in an oxygen atmosphereat a temperature of 450° C.; and the conductive oxide 72 having aperovskite structure represented by SrRuO₃ was formed thereon to athickness of 1,000 Å by sputtering at a temperature of 650° C. On thelower electrode 33, there was formed a ferroelectric layer of(Bi₂O₂)²⁺(SrTa₂O₇)²⁻ containing an amorphous Si compound in the samemanner as in the first embodiment. The orientation of the ferroelectricthin film was examined by X-ray diffraction, which gave the result inwhich the C-axis was tilted 45°. Further, the pole figure measurementusing a diffraction peak of the (105) face showed that the degree oforientation was 93%.

Next, a configuration of an upper electrode in this embodiment is shownin FIG. 8(a). An upper electrode 31 includes a conductive oxide 82having a perovskite structure, a conductive oxide 83 of a singleelement, and a metal 84. Like the case of using the conductive oxide asthe lower electrode, the above upper electrode 31 was effective tosuppress an oxygen loss layer having been generally recognized at aninterface between a ferroelectric material and a metal electrode. Aconductive oxide having a perovskite structure, represented by SrRuO₃,was formed on the above ferroelectric layer of (Bi₂O₂)²⁺(SrTa₂O₇)²⁻containing an amorphous Si compound to a thickness of 1,000 Å bysputtering in an oxygen atmosphere at a temperature of 650° C. Further,the conductive oxide 83 of a single element, represented by RuO, wasformed thereon to a thickness of 1,000 Å by sputtering in an oxygenatmosphere at a temperature of 450° C., and then the metal 84represented by Ru was formed thereon to a thickness of 1,000 Å bysputtering at a temperature of 600° C. The ferroelectric elementexhibited good ferroelectric characteristics. For example, the leakagecurrent density was 1×10⁻⁸ A/cm² at 5 V; 2Pr was 16 μC/cm² at 3 V and Ecwas 40 kV/cm; and degradation of characteristic was about 5% afterrewriting 10¹⁵ times by positive/negative reversal of a voltage of 3 V.

Although in this embodiment (Bi₂O₂)²⁺(SrTa₂O₇)²⁻ was used as theferroelectric material, it is also possible to use the ferroelectricmaterial expressed by the chemical structural formula of(AO)²⁺(B_(y−1)C_(y)O_(3y+1))²⁻ or the ferroelectric material expressedby the chemical structural formula of (Pb_(1−x)A_(x))(Zr_(1−y)Ti_(y))O₃in the first embodiment, or the high dielectric material expressed bythe chemical structural formula of (Ba_(1−x)Sr_(x))TiO₃ in the secondembodiment.

With respect to the above upper and lower electrodes, specific examplesof the metal may include Pt, Au, Al, Ni, Cr, Ti, Mo, and W; specificexamples of the conductive oxide of a single element may includeTiO_(x), VO_(x), EuO, CrO₂, MoO₂, WO₂, RhO, OsO, IrO, PtO, ReO₂, RuO₂,and SnO₂; and specific examples of the conductive oxide having aperopvskite structure may include ReO₃, SrReO₃, BaReO₃, LaTiO₃, SrVO₃,CaCrO₃, SrCrO₃, SrFeO₃, La_(1−x)Sr_(x)CoO₃ (0<x<0.5), LaNiO₃, CaRuO₃,SrRuO₃, SrTiO₃, and BaPbO₃.

Further, after formation of the lower electrode, and a ferroelectricthin film or a high dielectric thin film in the same manner as describedabove, another upper electrode of the present invention shown in FIG.8(b) was formed, as follows. Like the above embodiment, a conductiveoxide 82 having a perovskite structure, represented by either of ReO₃,SrReO₃, BaReO₃, LaTiO₃, SrVO₃, CaCrO₃, SrCrO₃, SrFeO₃,La_(1−x)Sr_(x)CoO₃ (0<x<0.5), LaNiO₃, CaRuO₃, SrRuO₃, SrTiO₃, and BaPbO₃was formed to a thickness of 1,000 Å by sputtering in an oxygenatmosphere at a temperature of 650° C., and then a metal 84, representedby either of Pt, Au, Al, Ni, Cr, Ti, Mo, and W was formed to a thicknessof 1,000 Å by sputtering at a temperature of 600° C., to form an upperelectrode, thereby preparing a ferroelectric element or a highdielectric element.

Embodiment 4

Although a metal alkoxide is used as a starting material forspin-coating for forming a high dielectric thin film in each ofEmbodiments 1 to 3, a ferroelectric thin film or a high dielectric thinfilm can be prepared by spin-coating using as a starting material ametal acetyleacetonato, a metal carbonate, an acetate, or a metal soapsuch as a metal naphthenate or metal octylate.

Similarly, a ferroelectric thin film or a high dielectric thin film canbe prepared in the same process as described above by dip-coating usingas starting material a metal alkoxide, a metal acetyleacetonato, a metalcarbonate, an acetate, or a metal soap such as a metal naphthenate ormetal octylate.

In preparation of a ferroelectric thin film or a high dielectric thinfilm in each of Embodiments 1 to 3, a ferroelectric thin film or a highdielectric thin film having a thickness of 1,000 Å was obtained bysputtering in an atmosphere containing oxygen gas at a pressure of 0.02to 10⁻⁴ torr at a temperature of 530 to 650° C. for 1 hr.

Also, in preparation of a ferroelectric thin film or a high dielectricthin film in each of Embodiments 1 to 3, a ferroelectric thin film or ahigh dielectric thin film having a thickness of 1,000 Å was obtained bylaser vapor-deposition using a sintered body having the same compositionas that of the above high dielectric thin film in an atmospherecontaining oxygen gas at a pressure of 0.3 to 10⁻⁴ torr at a temperatureof 530 to 650° C. for 1 hr.

Further, in preparation of a ferroelectric thin film or a highdielectric thin film in each of Embodiments 1 to 3, a ferroelectric thinfilm or a high dielectric thin film having a thickness of 1,000 Å wasobtained by MOCVD using β-diketone complex compound, or phenyl-group oro-tolyl group compound as a starting material in an atmospherecontaining oxygen gas at a pressure of 0.3 to 10⁻⁴ torr at a temperatureof 530 to 650° C. for 2 hr.

In the above laser vapor-deposition or MOOCVD process, a ferroelectricthin film or a high dielectric film having a thickness of 1,000 Å wasobtained in an atmosphere containing excited oxygen (ozone, ECR ormicrowave plasma) at a pressure of 0.3 to 10⁻⁴ torr at a temperature of500 to 620° C. for 1-2 hr.

Further, in preparation of either of a metal, a conductive oxide of asingle element, a conductive oxide of a perovskite structure in eachembodiment, by carrying out the same process as described above, it ispossible to use a metal, a conductive oxide of a single element, aconductive oxide of a perovskite structure like the above examples inthis embodiment.

Embodiment 5

FIG. 9 is a view showing a semiconductor device including aferroelectric element. The semiconductor device is prepared in thefollowing manner. First, a diffusion layer 97 is formed on an Si wafer95 by ion implantation and heat-treatment; an SiO₂ gate film 99 isformed thereon by surface oxidation; and a gate electrode 98 is formedthereon. After formation of an SiO₂ film 94 and an SiO₂ film 96 forelement isolation between a transistor and a capacitor, an aluminuminterconnection 910 is formed to connect an upper electrode 91 to thediffusion layer 97. As a ferroelectric element, a structure includingthe upper electrode 91, a ferroelectric thin film 92 and a lowerelectrode 93, which was prepared in Embodiments 1 to 4, was formed toobtain a semiconductor device including the ferroelectric element. Thesemiconductor device including the ferroelectric element thus obtainedenables detection by a change in stored charge capacitance obtained at avoltage of 3 V.

Although this embodiment has a structure including the upper electrode91, ferroelectric thin film 92, and lower electrode 93, there may beformed a high dielectric element having a structure including an upperelectrode, a high dielectric thin film, and a lower electrode. Thesemiconductor device including the high dielectric element thus obtainedhas a storage charge capacitance of 30 fF at a voltage of 3 V.

As described above, according to the present invention, there can beprovided a highly integrated ferroelectric element having a high Pr anda low Ec and having a good withstand voltage, in which a ferroelectriclayer thinned to a thickness of 200 Å or more is sandwiched betweenelectrodes, wherein the ferroelectric layer contains insulatingparticles to suppress leakage current caused through grain boundaries ofcrystals.

As described above, according to the present invention, there can beprovided a high dielectric element having a high dielectric constant anda good withstand voltage, which is thinned to a thickness of 200 Å ormore and includes a high dielectric layer, wherein the ferroelectriclayer contains insulating particles to suppress leakage current causedthrough grain boundaries of crystals.

A semiconductor device including a ferroelectric element can be formedby incorporating the above ferroelectric element in a field effecttransistor structure.

Further, a semiconductor device including a high dielectric element canbe formed by incorporating the above high dielectric element in a fieldeffect transistor structure.

As described above, this invention is effective, when applied to ahighly integrated ferroelectric element or high dielectric element, anda semiconductor device using the same.

What is claimed is:
 1. A dielectric element comprising an upperelectrode, a dielectric thin film, and a lower electrode, wherein saiddielectric thin film contains insulating particles having a resistancenot smaller than 10⁶ Ω, wherein said dielectric thin film comprises atleast one of a ferroelectric thin film and a high dielectric thin filmand wherein said ferroelectric thin film has a c-axis with anorientation that is tilted 45° to an electrode plane and has a degree oforientation that is at least 90%.
 2. A dielectric element according toclaim 1, wherein said insulating particles each have a particle size notlarger than 50 Å.
 3. A dielectric element according to claim 2, whereinsaid ferroelectric thin film is made of one kind selected from the groupconsisting of a material expressed by (Pb_(1−x)A_(x))(Zr_(1−y)Ti_(y))O₃(where A is one kind selected from the group consisting of La, Ba, andNb), and a material expressed by (AO)²⁺(By_(y−1)C_(y)O_(3y+1))²⁻ (whereA is at least one kind selected from a group consisting of Tl, Hg, Pb,Bi, and rare earth elements; B is at least one kind selected from thegroup consisting of Bi, Pb, Ca, Sr, and Ba; C is at least one kindselected from the group consisting of Ti, Nb, Ta, W, Mo, Fe, Co, Cr andZr; and y=2, 3, 4, and 5).
 4. A dielectric element according to claim 2,wherein said insulating particles are those of a chemical compoundcontaining Si.
 5. A dielectric element according to claim 4, whereinsaid ferroelectric thin film has a thickness of 200 Å or more, and saiddielectric element exhibits a withstand voltage not lower than 2 V at aleak current density not larger than 10⁻⁵ A/cm².
 6. A dielectric elementaccording to claim 1, wherein said metal is at least one kind selectedfrom the group consisting of Pt, Au, Al, Ni, Cr, Ti, Mo, and W.
 7. Adielectric element according to claim 1, wherein said conductive oxideof a single element is an oxide of at least one kind selected from thegroup consisting of Ti, V, Eu, Cr, Mo, W, Rh, Os, Ir, Pt, Re, Ru and Sn,and has a resistivity not larger than 1 mΩ·cm.